[R-390] Tube bulb temperatures

[Bob Camp]

Hi,

The gotcha here is that glass is more or less transparent. A good 
infrared thermometer is calibrated for an emisitivity of around 95%. 
That's a nice black surface, but not quite perfect. Depending on the 
characteristics of the glass at infrared you may or may not see it at 
all. If you do see it then you need to know what it's emisitivity (wish 
I knew how to spell that ...) is at the magic wavelength your 
thermometer is measuring.

One way around the whole problem is to grab a "known good" can of flat 
black paint and spray everything in sight with a couple of coats of it. 
Then you can assume you are seeing the paint and your readings are 
uniform.

How to make sure your paint is "known good" - carbon black is pretty 
much the standard of comparison. Spray a surface with your paint and 
then smoke a portion of the same painted surface. If you can see a 
temperature difference between the smoked area and the paint then try 
another brand of paint.

The worst thing to go after is anything with gold plating on it. Gold 
is a crummy infrared emitter. If you really want to give your paint a 
work out spray it on any gold bars you might have lying around the 
house. You should get a nice contrast between the painted and unpainted 
areas. I would be happy to confirm your measurements if you send me the 
gold bars after you measure them ...

The whole "black paint isn't  black" thing is the basis for the 
"better" performance of the IERC heat dissipating tube shields. The 
black varnish on the competitors parts wasn't black enough at infrared 
to make them work as well .....

	Take Care!

		Bob Camp
		KB8TQ




On Mar 21, 2004, at 1:23 PM, Bernie Nicholson wrote:

> The best and most convenient way to measure tube bulb temps is with a 
> Infrared thermometer they are quiete cheap and very accurate and u 
> dont have to make contact with the glass I measured the temp of the 
> radiator on my 4cx1000a  which is 3000 volts above earth the other 
> day,  and heat sinks are also easy to measure ,the unit contains a 
> Laser pointer  and electricians use them to measure the case temp of 
> transformers on power poles without climbing the pole regards to 
> everyone  73 s VK2ABN
>
>
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